(1) Field of the Invention
The present invention relates to processes used to fabricate semiconductor devices, and more specifically to a process used to define metal structures, via dry etching procedures, using photoresist shapes as an etch mask.
(2) Description of Prior Art
As the density of semiconductor chips increase, the width of metal interconnect structures have to be decreased. The critical dimensions of specific chip features, such as metal interconnect structures, are usually defined via dry etching procedures, using photoresist shapes as an etch mask. However, as the width of specific chip features, such as metal interconnect structures, decrease, the thickness of the defining photoresist shape also has to be decreased. The decreasing thickness for the defining photoresist shapes, makes it imperative that the etch selectivity, or etch rate ratio, between the metal being patterned, and the defining photoresist layer, remain high.
This invention will describe a process for defining narrow width, metal structures, for advanced semiconductor devices, via a dry etching procedure, using a photoresist shape as an etch mask. However this invention will describe a plasma treatment, in a nitrogen containing ambient, applied to the photoresist shape, prior to the metal etch cycle. The plasma treatment of the photoresist shape, slows the removal rate, of the photoresist shape, in a specific etchant, while maintaining the desired removal rate of the exposed metal. The increased etch rate selectivity allows thinner photoresist shapes, and thus narrower metal lines, to be realized. Prior art, such as Tsai et al, in U.S. Pat. No. 5,688,719, use a hydrogen containing plasma to harden the defining photoresist shape, prior to metal patterning, while Lo, in U.S. Pat. No. 5,726,102, uses an oxygen, or a nitrogen--oxygen ambient for treated defining photoresist shapes. However this invention, using only a nitrogen containing plasma, for treatment of photoresist shapes, offers the desired etch rate selectivity, between metal and photoresist, needed for definition of the narrow width, metal structures, used in advanced semiconductor devices.